THE STANDARD METABOLISM OF THE ORGANISM 57 



vestigations made upon isolated organs, and especially upon muscles, 

 it has been shown that a certain minimum or " basal " metabolism 

 involving respiratory exchange is inseparable from the life of every 

 organ, and will persist when the organ is doing no work whatever 

 so long as the ability to do work remains. 



The basal metabolism of an organ is not a constant quantity, but 

 can be modified experimentally by varying the external conditions (e.g. 

 the temperature) and may probably vary also from internal causes. 



When an organ is doing work the metabolic processes are invariably 

 increased, and incases where it has been possible to measure the work 

 a certain proportionality is observed between the work and the increase 

 in metabolism above that basal amount which corresponds to the con- 

 ditions of the moment. 



In the organism as a whole in which the functional activity can- 

 not be brought to a complete standstill we cannot determine basal 

 metabolism in the strictest sense of that term, but we may obtain an 

 approximation to it which can be defined as the metabolism correspond- 

 ing to a minimum functional activity. This is often termed basal met- 

 abolism (" Grundumsatz," Magnus-Levy [v. N.]), or maintenance met- 

 abolism ("Erhaltungsumsatz," Loewy [Op.]). I do not consider any 

 of these terms as very appropriate ; the first because we can only get an 

 approximation, and not even a close one, to the true basal metabolism, 

 and the second because the metabolism in question has nothing to do 

 with the maintenance of the organism, which certainly cannot be main- 

 tained upon it for any length of time. I shall prefer to call the met- 

 abolism as defined above the " standard metabolism " (Krogh, 1914, 2), 

 implying simply that all variations in metabolism brought about by 

 functional activity have to be referred to this quantity as a standard. 



In practice the minimum functional activity is taken to be at- 

 tained when voluntary muscular movements are eliminated and no 

 food is being digested or absorbed. 



The influence of digestion and absorption of food is in most cases 

 easy to eliminate, though certain herbivorous animals cannot be with- 

 out food for a sufficient time so as to eliminate it completely, but the 

 muscular movements are often difficult to exclude, and the value of a 

 large number of experiments in which the maintenance of standard 

 conditions was essential has been seriously impaired because muscular 

 movements were not rigorously excluded. In man the muscular 

 movements are excluded by willed muscular inactivity (" vorsatzlicher 

 Muskelruhe," Johansson [1897]) or during sleep. In animals the com- 



